Proteoglycans constitute only a small portion of the connective tissue of lung parenchyma, but perhaps through interactions with collagen and elastin are thought to play an important role in maintaining the structural and functional integrity of this tissue. We have developed a reproducible procedure for the extraction and purification of proteoglycans from fresh bovine lung after carefully removing all bronchi and large blood vessels. The properties of the isolated lung proteoglycans considerably differ from those of cartilage proteoglycans. We are now interested in exactly defining the chemical and physical characteristics of the isolated lung proteoglycans. By using enzymatic and immunological techniques we are trying to determine whether one or more proteoglycan species exist in the lung tissue and whether some proteoglycans resist extraction perhaps because of their association with other tissue components. This work is at the present time done using bovine lung because of its easy availability in sufficient quantity and we plan to eventually apply the knowledge thus acquired to the study of human normal and diseased (fibrotic, emphysematous) lungs.